Manual transfer switches are sufficient for most applications where, during a utility power outage, a homeowner, landlord, or property manager is available to startup a generator, make the necessary temporary electrical interconnections, and operate the transfer mechanism. This type of system is popular in part because of its simplicity and the modest equipment and installation costs involved.
However, such a manually actuated transfer system may not be suitable in some cases, particularly when no one is in attendance or where more convenience is desired or required. In such cases, a fully automatic transfer switch, operating in conjunction with a permanently installed alternate power source (such as a generator) might be preferred. The need for an electrical transfer device to safely switch between utility and generator power is well documented.
U.S. Pat. No. 6,031,193, the entire disclosure of which is incorporated herein by reference, describes an interlock arrangement for interlinking circuit breakers. This patent describes an interlock structure that causes the handle of a circuit breaker to first move a switch to an OFF position in response to an operator pushing the handle of an opposite circuit breaker to an ON position. In this regard, both circuit breakers cannot simultaneously be in the ON position. The result is that power cannot be supplied to a panel bus from two sources at one time, and one source cannot back-feed the other. Heretofore, such interlock structures have been limited to manual transfer switches.